Structure and Dynamics of Nothofagus Forests Near Timberline in South‐Central Chile

The dynamics of Northofagus forests in the near—timberline zone of south—central Chile are interpreted from structural analyses of pure stands, of Northofagus pumilio (Poepp. et Endl.) Krasser and mixed stands of N. betuloides (Mirb.) Bl. and N. pumilio. Nested quadrat pattern analyses suggest that the spatial distributions of these tree species are greatly affected by massive disturbances which periodically create conditions favorable for their regeneration. Their spatial distributions are also significantly affected by intra— and interspecific plant interactions. For example, as a stand ages, initially clustered distributions of saplings become regular or random as a consequence of the relatively large canopy space required by the shade—intolerant Northafagus. Strong community control of vegetation is also indicated by the inhibition of tree regeneration by the abundant understory bamboo, Chusquea tenuiflora Phil. In general, in the near—timberline Northofagus forests tree regeneration depends either on periodic, massive disturbance (by mass movements, volcanic ash desposition, avalanches, or large treefalls) or on the synchronous flowering and subsequent mass die—off of the local population of C. tenuiflora.